none Main bioecological aspects of Clostera anastomosis (L.) were studied during the period 1986 - 1998 in Bulgaria. This insect was recorded in relatively low population density in many localities of the country. It was found as a phylophage of Populus deltoides Marsh., P. tremula L., some poplar hybrid clones, Populus [x] euramericana (Dode) Guinier, and Salix fragilis L. The egg-masses of C. anastomosis contained an average of 147[plus/minus]29 eggs. The fecundity of the females varied from 332 to 746 eggs, with an average of 448[plus/minus]63 eggs. In laboratory conditions eggs hatched in 7 - 9 days. To complete their development, the larvae needed 18 - 26 days. There were five larval instars for male individuals and six larval instars for the females. Pupal period ranged from 8 to 12 days. In studied years C. anastomosis developed three generations annually and overintered as second-instar larvae. Three primary and two secondary parasitoids of C. anastomosis were found. Telenomus sp. (Hymenoptera: Scelionidae) parasitized an average of 7.3% of the host eggs. The remaining species, Glyptapanteles liparidis (Bouche) (Hymenoptera: Braconidae), Eriborus terebrator Aubert, Itoplectis alternans (Grav.) (Hymenoptera: Ichneumonidae) and Brachymeria sp. (Hymenoptera: Chalcididae) were larval parasitoids. The most effective was the gregarious species G. liparidis which destroyed 5.9-40% of the early- and mid-stage pest larvae. The number of parasitoid larvae feeding in a host was 7 - 16, with an average of 11.2[plus/minus]0.9. E. terebrator was found as a parasitoid of C. anastomosis only in Bulgaria. Sometimes it parasitized 16.6 - 27.5% of the early-stage (up to third instar) pest larvae. However, its effectiveness was reduced by hyperparasitoids I. alternans and Brachymeria sp. Nutrition; Diet; Life cycle and development; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Land and freshwater zones; Palaearctic region; Europe Clostera anastomosis (Notodontidae); Food plants; Populus & Salix; Life cycle; Phenology; Hymenopteran parasites; Parasite pathogenicity; Hyperparasitism; Brachymeria & Itoplectus (Hymenoptera); Bulgaria, food plant spectrum & hymenopteran parasites Hymenoptera; Hymenopteran parasites; Brachymeria & Itoplectus; Lepidopteran hosts; Clostera anastomosis; Pathogenicity & hyperparasitism by Hymenoptera; Hyperparasitism; Brachymeria & Itoplectus (Hymenoptera); Hyperparasitism in Lepidoptera; Bulgaria; Lepidopteran hosts & hyperparasitism by Hymenoptera Itoplectis alternans (Ichneumonidae ); Brachymeria (Chalcididae ); Hymenopteran hosts; Hyperparasitism; Of Hymenoptera in lepidopteran host; Bulgaria; Hyperparasitism in hymenopteran parasites of Lepidoptera